Ric, I posted the link below to what I believe is the Buckeye page for their Purifi 1ET9040BA based monoblocks. Scroll down to the Custom I/O Board: heading where he lists the TI OPA1656 OP Amp.
[EDIT]: Even the Purifi 1ET9040BA PDF data sheet is a bit confusing. It shows the module gain as 14.4 dB so you're left to assume that the overall gain is due to the op-amp input which has 3 settings. The datasheet also shows the module input Z as 1.5kOhm diff & 1.3kOhm single-ended. I have to assume that the higher input Z is from the input of the op-amp and I further assume that it will vary depending on what input resistor values the builder chooses to use??? Big question mark.
